It is now in wide use to make fibers having a water and oil repellency, using a water and oil repellent comprising a (meth)acrylate copolymer containing a polyfluoroalkyl group, mostly a perfluoroalkyl group, as an effective component. (Meth)acrylate containing a perfluoroalkyl group (Rf group) can be made from a compound Rf I through various reactions, where the perfluoroalkyl iodide Rf I can be synthesized by telomerization of C2F5I as a starting material, and the resulting product is a mixture of compounds represented by the general formula CnF2+1, with a distribution in chain lengths of various n values.
Generally, components C6F13I to C14F29I are used as effective components, whereas components C16F33I or higher n value components have no effective utility and components C12F25I˜C14F29I are discarded because of the imbalance between the production and the consumption. From the viewpoints of recent environmental protection control and economy, on the other hand, effective utilization of these unutilized resources and discarded components is now highly desirable. Preparation of an aqueous dispersion of (meth)acrylate polymers containing C12F25 or longer chain Rf groups has such a problem that the resulting aqueous dispersion has an unsatisfactory emulsion stability.
In the case of preparing aqueous dispersion of (meth)acrylate copolymers containing perfluoroalkyl groups, it has been so far proposed to add triethyleneglycol dimethyl ether, tetraethyleneglycol dimethyl ether, dipropyleneglycol, 1,6-hexanediol, 1,5-pentanediol, diethyl succinate, etc. thereto (JP-B-4-32873, JP-B-6-74409 and U.S. Pat. No. 6,180,740), but these methods have been found that the aqueous dispersions of (meth)acrylate copolymers containing mixed perfluoroalkyl groups including perfluoroalkyl groups of 12 or more carbon atoms, particularly 16 or more carbon atoms have quite an unsatisfactory emulsion stability.
The present applicant proposed earlier a process for preparing an aqueous emulsion by subjecting (meth)acrylate containing a polyfluoroalkyl group and stearyl (meth)acrylate to emulsion polymerization at a pH of 2 to 5.5 with a betaine-type emulsifier and a nonionic emulsifier (JP-A-11-255,995), but further improvements have been found still necessary with respect to the emulsion stability of aqueous dispersion, typically weight percent precipitate, 10% particle size, 50% particle size, 90% particle size, etc.